1. Technical Field
The present invention relates to a printing data generating apparatus that generates printing data for causing a printer to perform printing.
2. Related Art
Ink jet printers perform printing by repeatedly performing a main scanning operation and a sub scanning operation. In a main scanning operation, while moving a print head having a plurality of nozzles in a predetermined direction, ink is ejected from each of the nozzles. Thus, a plurality of lines are printed on a printing medium. After completion of printing of the plurality of lines, a sub scanning operation is performed in which the print head is moved in a direction perpendicular to the above-mentioned predetermined direction. Further, in order to achieve printing at high resolution by printing dots at intervals less than the intervals at which the nozzles are arranged, there has been developed a technique for printing a line in the N-th main scanning operation between lines printed in the (N−1)-th or earlier main scanning operations (see, for example, JP-A-2002-292908).
With the technique disclosed in JP-A-2002-292908, however, it is impossible to prevent a misalignment between the position of a line printed at an earlier timing and the position of a line printed at a later timing. That is, in the ink jet printers, once ink has been ejected onto a printing medium, the ink penetrates into the printing medium, so that the printing medium becomes more likely to expand. In the case of performing a plurality of main scanning operations to complete printing of a plurality of lines, a large amount of ink has already been penetrated into a printing medium when the last main scanning operation is performed. Accordingly, when the last main scanning operation is performed, the printing medium is expanded by a greater degree than when the earlier main scanning operations were performed. This results in a misalignment between the position of the lines in the earlier main scanning operations and the position of the lines in the last main scanning operation. Such misalignment is more pronounced when a greater number of nozzles are provided in a print head. Accordingly, in the case of printers having a print head of such a size that printing is possible from one edge to another edge of a printing medium, such misalignment is significantly pronounced.